How can I decide the primary current of the Zero-sequence CT?
How can I decide the primary current of the Zero-sequence CT?
(OP)
Dear everyone:
Would you like to give me some hint about how can I decide the primary current for the zero-sequence CT? In my concept, only in the condition of earthing fault or 3 phases is unbalanced, the zero-sequence current created and normarlly it will big especial when the 1 phase directly earthed. but how to calculated the primary current?
you will be highly appreciated.
Thank you.
Forward
Would you like to give me some hint about how can I decide the primary current for the zero-sequence CT? In my concept, only in the condition of earthing fault or 3 phases is unbalanced, the zero-sequence current created and normarlly it will big especial when the 1 phase directly earthed. but how to calculated the primary current?
you will be highly appreciated.
Thank you.
Forward





RE: How can I decide the primary current of the Zero-sequence CT?
RE: How can I decide the primary current of the Zero-sequence CT?
RE: How can I decide the primary current of the Zero-sequence CT?
Thanks a lot.
RE: How can I decide the primary current of the Zero-sequence CT?
The secondary current rating must be determined from the input range of the GF relay being used. The primary rating, as I have said, typically has a continuous rating equal to the circuit being monitored.
RE: How can I decide the primary current of the Zero-sequence CT?
If the system is solidly-grounded, a higher ratio - 200/5 may be in order. For resistance grounded systems, a 50/5 might be more appropriate.
If you are trying to selectively trip overcurrent relays based on this current, then saturation is a concern. If selectivity isn't an issue, then ac saturation isn't as big a problem.
50/5 is very commonly used for this application on feeder circuits.
RE: How can I decide the primary current of the Zero-sequence CT?